Flat Roof Insulation Thickness

Achieving greater r values in attics the higher the r value the better the thermal performance of the insulation.

Flat roof insulation thickness.

U value of a flat roof to comply with part l of the building regulations 2010 all roofs to rooms except those in unheated buildings should be thermally insulated to a maximum u value of of 0 18 w m k. With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same. Achieving a u value of 0 20w m meaning your roof will be better insulated than your walls will need 120mm thickness of rigid foam or 200mm of mineral wool or natural insulation. However if we do not include removal of old roofing you are looking at about 7 50 to 9 00 per foot of roofing plus about 2 50 to 3 00 per foot of 5 thick insulation say about 10 12 per square foot.

Better to have 3 or more. A lower u value indicates better insulation properties hence u value requirements usually specify a maximum value. If you are upgrading the roof to meet current thermal requirements then the thickness of insulation will vary depending on its thermal conductivity. The typical u value of an existing uninsulated flat roof is 1 5w m2k.

Rockwool products are available with a bitumen or mineral coated fiberglass face to be used in a number of roofing solutions. It should be of the maximum available thickness. Since your attic is insulated i would advise at least 2 of polyiso insulation in the roof for good measure. As for insulation thickness it depends on how much you can afford.

Recommended roof insulation r value is 38 r but ideal is to have 50 r or more. Rockwool stone wool roof insulation combines the thermal performance dimensional stability impact resistance and acoustic control required to increase the performance of many flat roof assemblies.